The full extent of the problems facing blood transfusion services from possible contamination by the human form of BSE is revealed for the first time today.

At least 48 people have received red blood cells or other blood components from 15 people who went on to develop the human form of BSE.

Details in the Lancet coincide with a warning from an adviser to the government that there is a "very small" chance that the only variant CJD death so far tentatively linked to blood donation is not transfusion-related. That person was old compared to other victims of the disease conventionally linked to eating infected meat products usually consumed by younger people.

Most of the known recipients of transfusions have died from other causes, half within a year of transfusion, but two of the 17 still alive had transfusions within the last three years from donors who had already begun to show difficult-to-interpret signs of variant CJD. Other donors were only a few months from displaying symptoms.

Other research has suggested that might mean people who received donations from people with long-developed infection were exposed to more infectious doses through the blood donations. Ten of the 17 still-living recipients have now lived more than five years after their transfusions.

One person in their late 60s died from vCJD last autumn, possibly as a result of a contaminated blood transfusion more than seven and a half years before. The victim was the second oldest among the 139 Britons who have died plus seven still alive. The oldest was 74, with most well under 40 and some in their teens.

The vCJD donor in the implicated case was 24 and the transfusion happened in 1996, three years before the person developed signs of the disease which led to death in 2000. Four other units of blood from other donors were used.

The announcement of the death, but not the ages of recipient or donor, was made just before Christmas and only now are full details of potential problems publicly detailed by researchers from the CJD surveillance unit in Edinburgh and the national blood service.

They say that although the British epidemic of vCJD "seems to be in decline, a proportion of the UK population could be incubating vCJD and acting as blood donors".

Other government advisers are urgently considering whether to bar all people who have received transfusions being blood donors as a result of the recent death. Estimates have suggested that could cut donors by between 3% and 15%.

There is another complication. The vCJD-incubating donors who gave red blood cells, platelets and other components also gave 20 units of plasma, then mixed with thousands of other donations into clotting factors for people with haemophilia. The risks from these blood products are probably far smaller than from normal transfusions but no-one knows how many people have had them. Some were exported before British sources were abandoned five years ago.

People needing transfusions are often old and extremely ill, meaning that the benefits of transfusion have to be balanced against unquantifiable risk from contracting a disease always fatal, but still rare.

The researchers are cautious about the extent of the risk from the blood transfusions. "Although statistical analysis suggests that coincidence is an unlikely explanation for this case, it is important to stress that this is a single case and there is the possibility that infection was due to dietary exposure to the BSE agent, the presumed route of animal to human transmission of BSE."

But a commentary from Adriano Aguzzi, an advisor to the government on vCJD, and Markus Glatzel, his colleague at the University Hospital of Zurich, comments: "They do not present direct evidence that the disease was transmitted by blood transfusion, but the chance that this case is not transfusion-related is small."